angular.element('input[ng-model="b.LastStake.UnitPriceOriginal"]').val('500').change();
angular.element('input[ng-click="makeStake(stakeForm, b.Bid.BidId, b.LastStake.UnitPriceOriginal, b.curCurrencyId, b.LastStake.SuggestedDelay, b.LastStake.Quantity, b.LastStake.Info)"]').click();
А тебе это зачем?